Mumble means not speaking clearly. Mumbling leads to unclear and indistinct conversation. The option that is closest in relationship to this is the option C as scribbling leads to illegible handwriting. The rest of the options are related in some different manner.
Swagger means to walk or behave in a very confident and arrogant way, whereas timid shows a lack of courage. So they are opposite to each other.
Exacerbate means makes something worse and cure is its opposite.
Drizzle is light rain whereas downpour is heavy rainfall.